Matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS=a disintegrin and metalloproteinase with thrombospondin motif) are a family of structurally related zinc-containing enzymes that have been reported to mediate the breakdown of connective tissue in normal physiological processes such as embryonic development, reproduction, and tissue remodelling. Over-expression of MMPs and aggrecanases or an imbalance between extracellular matrix synthesis and degradation has been suggested as factors in inflammatory, malignant and degenerative disease processes. MMPs and aggrecanases are, therefore, targets for therapeutic inhibitors in several inflammatory, malignant and degenerative diseases such as rheumatoid arthritis, osteoarthritis, osteoporosis, periodontitis, multiple sclerosis, gingivitis, corneal epidermal and gastric ulceration, atherosclerosis, neointimal proliferation (which leads to restenosis and ischemic heart failure) and tumor metastasis.
The ADAMTSs are a group of proteases that are encoded in 19 ADAMTS genes in humans. The ADAMTSs are extracellular, multidomain enzymes whose functions include collagen processing, cleavage of the matrix proteoglycans, inhibition of angiogenesis and blood coagulation homoeostasis (Biochem. J. 2005, 386, 15-27; Arthritis Res. Ther. 2005, 7, 160-169; Curr. Med. Chem. Anti-Inflammatory Anti-Allergy Agents 2005, 4, 251-264).
The mammalian MMP family has been reported to include at least 20 enzymes (Chem. Rev. 1999, 99, 2735-2776). Collagenase-3 (MMP-13) is among three collagenases that have been identified. Based on identification of domain structures for individual members of the MMP family, it has been determined that the catalytic domain of the MMPs contains two zinc atoms; one of these zinc atoms performs a catalytic function and is coordinated with three histidines contained within the conserved amino acid sequence of the catalytic domain. MMP-13 is over-expressed in rheumatoid arthritis, osteoarthritis, abdominal aortic aneurysm, breast carcinoma, squamous cell carcinomas of the head and neck, and vulvar squamous cell carcinoma. The principal substrates of MMP-13 are fibrillar collagens (types I, II, III) and gelatins, proteoglycans, cytokines and other components of ECM (extracellular matrix).
The activation of the MMPs involves the removal of a propeptide, which features an unpaired cysteine residue complexed with the catalytic zinc (II) ion. X-ray crystal structures of the complex between MMP-3 catalytic domain and TIMP-1 and MMP-14 catalytic domain and TIMP-2 also reveal ligation of the catalytic zinc (II) ion by the thiol of a cysteine residue. The difficulty in developing effective MMP inhibiting compounds comprises several factors, including choice of selective versus broad-spectrum MMP inhibitors and rendering such compounds bioavailable via an oral route of administration.
MMP-3 (stromelysin-1; transin-1) is another member of the MMP family (FASEB J. 1991, 5, 2145-2154). Human MMP-3 was initially isolated from cultured human synoviocytes. It is also expressed by chondrocytes and has been localized in OA cartilage and synovial tissues (Am. J. Pathol. 1989, 135, 1055-64).
MMP-3 is produced by basal keratinocytes in a variety of chronic ulcers. MMP-3 mRNA and Protein were detected in basal keratinocytes adjacent to but distal from the wound edge in what probably represents the sites of proliferating epidermis. MMP-3 may thus prevent the epidermis from healing (J. Clin. Invest. 1994, 94, 79-88).
MMP-3 serum protein levels are significantly elevated in patients with early and long-term rheumatoid arthritis (Arthritis Rheum. 2000, 43, 852-8) and in osteoarthritis patients (Clin. Orthop. Relat. Res. 2004, 428, 272-85) as well as in other inflammatory diseases like systemic lupus erythematosis and ankylosing spondylitis (Rheumatology 2006, 45, 414-20).
MMP-3 acts on components of the ECM as aggrecan, fibronectin, gelatin, laminin, elastin, fibrillin and others and on collagens of type III, IV, V, VII, IX, X (Clin. Orthop. Relat. Res. 2004, 428, 272-85). On collagens of type II and IX, MMP-3 exhibits telopeptidase activity (Arthritis Res. 2001, 3, 107-13; Clin. Orthop. Relat. Res. 2004, 427, S118-22). MMP-3 can activate other MMP family members such as MMP-1, MMP-7, MMP-8, MMP-9 and MMP-13 (Ann. Rheum. Dis. 2001, 60 Suppl 3:iii62-7).
MMP-3 is involved in the regulation of cytokines and chemokines by releasing TGFβ1 from the ECM, activating TNFα, inactivating IL-1β and releasing IGF (Nat. Rev. Immunol. 2004, 4, 617-29). A potential role for MMP-3 in the regulation of macrophage infiltration is based on the ability of the enzyme to convert active MCP species into antagonistic peptides (Blood 2002, 100, 1160-7).
MMP-8 (collagenase-2; neutrophil collagenase; EC 3.4.24.34) is another member of the MMP family (Biochemistry 1990, 29, 10628-34). Human MMP-8 was initially located in human neutrophils (Biochemistry 1990, 29, 10620-7). It is also expressed by macrophages, human mucosal keratinocytes, bronchial epithelial cells, ginigival fibroblasts, resident synovial and articular chondrodrocytes mainly in the course of inflammatory conditions (Cytokine & Growth Factor Rev. 2006, 17, 217-23).
The activity of MMP-8 is tightly regulated and mostly limited to the sites of inflammation. MMP-8 is expressed and stored as an inactive pro-enzyme in the granules of the neutrophils. Only after the activation of the neutrophils by proinflammatory mediators, MMP-8 is released and activated to exert its function.
MMP-8 plays a key role in the migration of immune cells to the sites of inflammation. MMP-8 degrades components of the extracellular matrix (ECM) such as collagen type I, II, III, VII, X, cartilage aggrecan, laminin-5, nidogen, fibronectin, proteoglycans and tenascin, thereby facilitating the cells migration through the ECM barrier. MMP-8 also influences the biological activity of its substrates. Through proteolytic processing of the chemokines IL-8, GCP-2, ENA-78, MMP-8 increases the chemokines ability to activate the infiltrating immune cells. While MMP-8 inactivates the serine protease inhibitor alpha-1 antitrypsin through its cleavage (Eur. J. Biochem. 2003, 270, 3739-49; PloS One 2007, 3, 1-10; Cytokine & Growth Factor Rev. 2006, 17, 217-23).
MMP-8 has been implicated in the pathogenesis of several chronic inflammatory diseases characterized by the excessive influx and activation of neutrophils, including cystic fibrosis (Am. J. Resprir. Critic. Care Med 1994, 150, 818-22), rheumatoid arthritis (Clin. Chim. Acta 1996, 129-43), chronic periodontal disease (Annals Med. 2006, 38, 306-321) and chronic wounds (J. Surg. Res. 1999, 81, 189-195).
In osteoarthritis patients, MMP-8 protein expression is significantly elevated in inflamed human articular cartilage in the knee and ankle joints (Lab Invest. 1996, 74, 232-40; J. Biol. Chem. 1996, 271, 11023-6).
The levels of activated MMP-8 in BALF is an indicator of the disease severity and correlates with the airway obstruction in patients with asthma, COPD, pulmonary emphysema and bronchiectasis (Lab Invest. 2002, 82, 1535-45; Am. J. Respir. Crit. Care Med. 1999, 159, 1985-91; Respir. Med. 2005, 99, 703-10; J. Pathol. 2001, 194, 232-38).